1. Field of the Invention
The present invention relates generally to electrolytic marking apparatus and, more particularly, is concerned with an electrolytic etching apparatus and method for marking metal tubes with sequential identification numbers.
2. Description of the Prior Art
In the manufacture of nuclear fuel rods, it is desirable at the start of the manufacturing process to temporarily mark the fuel rod cladding tubes for purposes of traceability through the process. A marking method capable of providing an identification marking on the tube without significantly disturbing the surface or metallurgical characteristics of the tube is desired.
One such method is electrolytic etching or marking which is well-known in the prior art. Representative of the prior art are the electrolytic marking apparatuses disclosed in Lindsay U.S. Pat. No. (2,967,813), Mayer U.S. Pat. No. (3,290,236) and Boulanger et al U.S. Pat. No. (4,132,618). In the apparatus of the Mayer patent, a metal part to be marked is supported on a base electrode. An absorbent pad attached to a head of an upper electrode located above the part is saturated with an electrolyte from an overhead reservoir. A stencil bearing the identification indicia is mounted in a holder attached to a vertically reciprocable member which also carries the upper electrode and overhead reservoir. The holder positions the stencil below the pad and above the part.
To electrolytically mark the part using the Mayer apparatus, the reciprocable member is lowered, causing the movable electrode head and pad thereon to press the stencil against the part. At this time, electrical energy is applied to the electrodes causing an electrolytic etching action to occur through the cooperation of the electrolytic solution and electrical energy operating through the stencil.
Although the Mayer apparatus might be suitable for marking some metal parts, it has drawbacks when applied to marking large numbers of tubes, such as nuclear fuel rod cladding tubes. Because the stencil used in the Mayer apparatus only contains one identification number and is held stationary by the apparatus holder, the stencil has to be replaced each time to apply a different identification number. As a result, use of this apparatus would be too slow and thus not feasible in conjunction with production of a large number of tubes with unique identification numbers. Also, the location of the electrolyte-saturated pad above the part would make it difficult to control the amount of electrolyte applied to the stencil and part with the likelihood being that the amount would be uneven and produce a non-uniform identification number.
Consequently, a need exist for a different approach to electrolytic marking of tubes which avoids the above-mentioned drawbacks.